Electric Vehicle Creep Torque Control for Smooth Range Shifts
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Solution Overview
Problem
Electric vehicles experience unnatural forward and rearward G variations when switching from a traveling range to a non-traveling range due to sudden release of creep torque stored in the drive shaft, leading to an unpleasant driving experience.
Innovation Solution
A control device for electric vehicles that includes a motor control system to stepwisely decrease creep torque and an automatic transmission control system to gently disengage the frictional engagement element, ensuring the transmission torque capacity remains greater than the decreased creep torque, thereby smoothing the transition and reducing G variations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the creep torque is cut immediately when the brake is operated to suppress electricity consumption, then energy efficiency is improved, but sudden G variation occurs causing unnatural driving feel
Solution Approach 1:
The control device determines in advance whether the vehicle is in a creep torque storage state before executing creep torque cut. When the shift range is switched from traveling range to non-traveling range while stopped, the system identifies this as a state where creep torque is stored in the drive shaft, and prepares to execute gradual torque reduction instead of immediate cut, preventing sudden G variation while still achieving energy savings.
Solution Approach 2:
The control device dynamically adjusts the creep torque reduction strategy based on the detected shift range and vehicle state. Instead of a fixed immediate cut, the system varies the torque reduction approach: gradual reduction when in non-traveling range to suppress G variation, and immediate cut in other conditions to maximize energy efficiency. This dynamic control resolves the contradiction between energy savings and driving comfort.
2Loss of time
If the brake sensor information is used before stroke learning is finished, then response time is improved, but control accuracy deteriorates
Solution Approach 1:
The control device performs stroke learning in advance during vehicle operation and stores the learned brake operation threshold values. When the vehicle is later stopped and shift range is switched to non-traveling range, the pre-learned stroke values are immediately available for accurate brake operation determination, eliminating the need to wait for stroke learning completion while maintaining detection accuracy.
Solution Approach 2:
The control device creates a copy of the brake operation detection logic that can function independently of the stroke learning process. By using the learned stroke threshold values as reference copies, the system can accurately determine brake operation status even when stroke learning is not currently active, ensuring both rapid response and accurate detection.
Data Source
Figure 1
Figure 2~3
Figure 4~5
AI summary
In a specific state where an electric vehicle is in a stop state and a creep torque is generate in an electric motor (2), when a shift range is switched from a traveling range to a non-traveling range, a motor control section (10B) performs a torque decrease control to stepwisely decrease the creep torque of the electric motor (2), and an automatic transmission control device (30) performs a disengagement control to gradually disengage the frictional engagement element of the automatic transmission (3).